[compiler-rt] Don't explicitly ad-hoc code sign dylibs if using Apple's new linker (#88323)

Apple's new linker reports itself as ld rather than ld64 and does not
match the version detection regex.

Invert the logic to look only for older versions of ld64. This ensures
the runtime dylibs are left with a linker-generated code signature that
tools such as `strip` will preserve.

Co-authored-by: Mark Rowe <markrowe@chromium.org>